Effect of Fertilizer on
Yield of Native Grass
By Eddie Funderburg and Jon T. Biermacher
Fertilization of native grass fields is
generally not recommended in the
Southern Great Plains region of the
United States. The primary reason for
not fertilizing native grass is the belief
that the benefit of fertilization is outweighed by the fertilizer and application costs. Native grass plant communities contain a mixture of grass,
broadleaf and woody perennial plant
species, and compose a large percentage of the forage base in this area.
A research project was developed
to determine the effect of fertilizer
rate on yield and profitability of native grass. The project had two locations: St. Louis, Okla., (Pottawatomie
County) and Ardmore, Okla. (Carter
County). The test at each location had
five fertilizer rates: 0-0-0, 50-0-0, 5050-0, 100-0-0 and 100-50-0 pounds
per acre of N-P2O5-K2O. Each location
was replicated three times. The test
was conducted in 2008 and 2009.
The soil series at the St. Louis site
was Aydelotte clay loam and the
soil series at the Ardmore site was
Weatherford fine sandy loam. Soil
test results showed very low levels
of phosphorus (Mehlich 3 soil test P
levels of 6 pounds per acre at the St.
Louis site and 8 pounds per acre at
the Ardmore site). The St. Louis site
had a better stand of native grass
than the Ardmore site, due to a
combination of past management
practices and more productive soil.
Fertilizer was applied to existing
stands of native grass in April of each
year. Fertilizer sources were ammonium nitrate (34-0-0) and diammonium phosphate (18-46-0). Plots
were harvested in mid-July of each
year and then again after frost. This
NF-SO-12-02
Derick Warren, Ag Research Assistant, harvests native grass plots at the St. Louis,
Okla. location.
was done to mimic either intensive
grazing or a hay harvest in early summer, then grazing after frost. Quality measurements for crude protein
and total digestible nutrients (TDN)
were collected at each harvest. An
economic analysis was conducted on
The Samuel Roberts Noble Foundation
each treatment to determine profitability. The economic analysis used
input prices and forage values that
were present at the time of the study.
Differences in input prices, forage values or both could change the results
of the economic analysis. Yields and4
SOILS
profitability rankings are shown in
Table 1.
Findings
Fertilizing native grass resulted in
large increases in yield. At both locations, applying 50 pounds of nitrogen
per acre produced yields as high as
those obtained with 100 pounds of
nitrogen per acre. It was essential
to apply phosphorus along with the
nitrogen to optimize yields on these
soils which have low soil test phosphorus levels.
There were no clear differences in
crude protein or TDN among fertilizer
treatments. All treatments produced
similar forage quality.
There were no significant differences in profitability among treatments except for the 100-0-0 per
acre fertilizer treatment. This treatment was less profitable than the
other systems. All other systems were
equally profitable within a 95 percent
probability level. When there is no
clear economic benefit to fertilization,
it is usually not recommended due
to increased risk associated with the
added cost.
We are currently evaluating the
test to see if there are carryover effects from the fertilizer treatments.
The plots were fertilized in 2008 and
2009, and were not fertilized after
Table 1. Effect of fertilizer rate on yield and profitability ranking of native grass
at two Oklahoma locations (two-year average 2008-09)
Location
Profitability Ranking
St. Louis, Okla.
Ardmore, Okla.
1= most profitable
Treatment
Yield (lbs dry matter forage per acre)
5 = least profitable
0-0-0
2536 D
1504 B
1A
50-0-0
3674 C
2213 B
3A
50-50-0
4648 AB
3720 A
4A
100-0-0
4014 BC
2161 B
5B
100-50-0
5212 A
4024 A
2A
those years. The plots were harvested
in 2010, and plots that received
phosphorus (P) in 2008-09 yielded
significantly more than any of the
other treatments. The plots were
harvested again in 2011, and there
were no yield differences in any of
the plots, but overall yields were very
low due to severe drought. We will
continue to harvest the plots each
year until yield differences between
plots disappear. This could revise the
profitability figures if there is a longterm carryover effect of fertilization.
Recommendations
1. If there is sufficient land area available to run the number of cattle
desired, do not fertilize native
grass. Economic analysis showed
that not fertilizing native grass
was as profitable as applying relatively large amounts of fertilizer.
2. If a rancher needs to increase
carrying capacity and does not
have introduced species such as
bermudagrass available to fertilize, an application of 50 pounds of
nitrogen per acre plus the amount
of phosphorus and/or potassium
recommended from soil test
results can roughly double the
carrying capacity of the land if
sufficient rainfall occurs to allow
the grass to fully utilize the fertilizer. Proper grazing management
must be incorporated into this
plan to ensure that overgrazing
does not occur.
3. If the decision is made to fertilize, soil tests from each field to
be fertilized are essential. Do not
fertilize without determining the
amount of phosphorus and/or
potassium that are needed along
with the nitrogen. <
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